Battery cooling apparatus for electric vehicle

ABSTRACT

A battery pack apparatus has a plurality of battery cell units that are stacked together in generally parallel relation. The battery cell units are configured to define converging air flow spaces therebetween. An air inlet header provides a converging air inlet plenum that is situated adjacent one side of the battery cell units and an air outlet header provides a diverging air outlet plenum that is situated adjacent an opposite side of the battery cell units. A blower or fan forces air into the air inlet plenum. The air flows through the air flow spaces between the battery cell units to cool the battery cell units. The speed of the air increases as it advances through the air inlet plenum and the plurality of air flow spaces.

BACKGROUND

The present disclosure relates to battery packs for automotive vehicles.More particularly, the present disclosure relates to battery coolingapparatus using air to cool battery packs having at least one stackedarray of rechargeable battery cells.

Electric vehicles, including hybrid electric vehicles, have electricmotors for propelling the vehicles along roadways, for example, andthese electric motors typically rely upon onboard rechargeable batteriesas their energy source. Battery packs having a fairly large number ofindividual rechargeable battery cells are frequently used with suchvehicles. An example of a battery cell that is used in electric vehiclesis a lithium ion battery cell. When recharging and when discharging toprovide power to the electric motors of electric vehicles, the batterycells generate heat that needs to be removed in order to maintain thebattery cells below their maximum allowable temperatures so that thebattery cells are not damaged or destroyed by the heat. When removingheat from battery packs, it is desirable but not necessary to have thefaces of each of the battery cells maintained at a fairly uniformtemperature.

Some electric vehicles may use liquid cooling systems to cool theirbattery packs. For example, liquid cooling systems using approximately50% ethylene glycol or other similar cooling fluids in water have beendeveloped. The cooling fluid is pumped or otherwise moved passed thebattery cells to remove the heat from the cells. The benefit of liquidcooling systems is that the volumetric heat capacity of the liquidallows tight control of temperature uniformity. However, liquid coolingsystems are heavy, costly, take up a lot of space, and are prone todeveloping fluid leaks, especially if they employ numerous fluidconnections.

Using air to cool battery packs, rather than liquid, introduces a hostof other concerns. Any cooling media possesses a finite thermal heatcapacity per unit of mass and will increase in temperature as it passesby the surface of the heat-generating item to be cooled, such as abattery cell. Air is a low-density cooling medium and can experiencehigh temperature gradients as it passes along a surface to be cooled ifthere is a poor ratio of air flow to heat absorption. In typical batterypack cooling systems in which air is used as the cooling media, near theinlet, the temperature of the battery cell face is approximately equalto the inlet air temperature and near the outlet, the temperature of thebattery cell face is approximately equal to the outlet air temperature.An example of a known air cooling system for a battery pack is shown anddescribed in U.S. Pat. No. 5,015,545. Often with these conventional aircooling designs, the air temperature increases across the face of thebattery cell by more than the preferred 3° Celsius for a lithium ionbattery, for example. Accordingly, there is a need for an improved aircooled battery pack apparatus.

SUMMARY

A battery pack apparatus for an automotive vehicle is provided andcomprises one or more of the features recited in the appended claimsand/or the following features which, alone or in any combination, maycomprise patentable subject matter:

A battery pack apparatus according to this disclosure may have aplurality of battery cells and a plurality of cell coverings. Thebattery cells may be generally flat battery cells. Each cell coveringmay have an internal space that receives at least one battery cell. Eachof the cell coverings may have external first and second planar facesthat face away from the at least one battery cell received in therespective internal space. The plurality of cell coverings may bearranged such that the first planar face of each cell covering faces thesecond planar face of an adjacent one of the plurality of cellcoverings. The first and second planar faces may be spaced apart fromone another. Each cell covering and the at least one battery cellcontained in the internal space of the cell covering may be referred toas a battery cell unit.

Each of the cell coverings may be constructed such that the first andsecond planar faces of adjacent cell coverings define a converging airflow space. Thus, the battery pack apparatus may have a plurality ofgenerally parallel converging air flow spaces that are defined betweenthe cell coverings. Each of the converging air flow spaces may be widerat an air inlet end of the air flow space and narrower at an air outletend of the air flow space.

Each of the cell coverings may have a plurality of standoffs extendingfrom the first and second planar faces to maintain proper spacingbetween adjacent pairs of cell coverings. In one embodiment, thestandoffs extending from the first planar face of each cell covering maycomprise a plurality of pedestals and the standoffs extending from thesecond planar face of each cell covering comprises a plurality ofpedestal receivers. The pedestals may have generally cylindricalportions and the pedestal receivers may comprise annular rings thatreceive the generally cylindrical portions of the pedestals. Thepedestals and pedestal receivers may be arranged to form a grid patternon the respective first and second planar faces. Rows of the griddefined by the pedestals and pedestal receivers may be substantiallyparallel with the top and bottom ends of the battery cell units or maybe skewed into an orientation that is inclined with respect to the topand bottom ends of the battery cell units. The standoffs may compriseribs that may be elongated and extend along the planar faces of the cellcoverings in a direction generally parallel to the direction of airflow.

Each of the cell coverings may include a tray-like first shell half anda tray-like second shell half. The first and second shell halves may beshaped to define the internal space therebetween and may mate togetheralong a peripheral seam that extends around the top, bottom and sides ofthe cell covering. The internal space may receive at least one batterycell therein. Each of the cell coverings may have first and secondsidewalls interconnecting the first and second planar faces. The firstand second sidewalls may have recesses formed therein to define a pairof upper ears situated above the recesses in the first and secondsidewalls and a pair of lower ears situated below the recesses in thefirst and second sidewalls.

Each of the upper ears and lower ears may have an aperture therethrough.The battery pack apparatus may include a set of coupling bars thatextend through the apertures in the pair of upper ears and pair of lowerears. According to this disclosure, each of the apertures may berectangular in shape and each coupling rod may have a rectangular crosssection. The battery pack apparatus may further include a first endplate and a second end plate. Each of the coupling bars may having afirst end fastened to the first end plate and a second end fastened tothe second end plate. Thus, as contemplated by this disclosure, theplurality of cell coverings and the plurality of battery cells may besandwiched between the first and second end plates of the battery packapparatus. The coupling bars may hold the cell coverings and batterycells in place thereby forming a stacked array of battery cell units.

The upper and lower ears may each have a protrusion on one side thereofand a depression on an opposite side thereof. The protrusions of theupper and lower ears of each cell covering may nest within thedepressions of the upper and lower ears of a next adjacent cellcovering. Some of the depressions and protrusions may be round in crosssection and at least one of the depressions and a least one of theprotrusions may be non-round in cross section. Such a configurationprevents the cell coverings from being stacked in an improperorientation.

In one embodiment, the internal space of each cell covering receives twobattery cells. A top of each cell covering may have a first opening anda second opening. The openings may be formed by notches provided at thetop of the cell coverings along the peripheral seam of the associated offirst and second tray halves. Each of the pair of battery cells receivedin the internal space of each cell covering may have a positive terminaltab that extends through the first opening of the respective cellcovering and may have a negative terminal tab that extends through thesecond opening of the respective cell covering.

The battery pack apparatus may also have a top plate assembly that issituated atop all of the cell coverings. The top plate assembly may havea first row of openings through which respective pairs of the positiveterminal tabs extend and may have a second row of openings through whichrespective pairs of the negative terminal tabs extend. The top plate maybe configured to electrically interconnect all of the battery cells to amain positive stud and to a main negative stud. In one embodiment, thepositive terminal tabs of the two battery cells received in the internalspace of each of each of the cell coverings are coupled together and thenegative tabs of the two battery cells received in the internal space ofeach of the cell coverings are coupled to together. In such anarrangement, the pair of battery cells in each internal space of eachcell covering are electrically coupled together in parallel. Also inthis embodiment, the parallel pairs of battery cells are electricallyconnected in series between the main positive terminal stud and the mainnegative terminal stud.

Thus, with the exception of the pair of battery cells having theirnegative terminal tabs coupled to the negative main terminal stud withno intervening battery cells therebetween and the pair of battery cellshaving their positive terminal tabs coupled to the positive mainterminal stud with no intervening batter cells therebetween, thepositive terminal tabs of the pairs of each of the battery cells arecoupled electrically to the pair of negative terminal tabs of the nextadjacent battery cell and vice versa. The top plate assembly may haveconductive brackets which electrically couple the positive and negativeterminals tabs of adjacent pairs of battery cells together.

According to this disclosure, the battery pack apparatus may furtherinclude a blower, an air inlet header situated adjacent a first side ofthe cell coverings, and an air outlet header situated adjacent a secondside of the cell coverings. The air inlet header may be shaped to definea converging air inlet plenum that narrows in the direction of air flowproduced by the blower. That is, the air inlet plenum may narrow orconverge in the downstream direction. The air outlet header may beshaped to define a diverging air outlet plenum that widens in thedirection of air flow out of the air outlet header. That is, the airoutlet plenum may widen or diverge in the downstream direction. The airinlet ends of the converging air flow spaces between the cell coveringsmay be in air flow communication with the converging air inlet plenumand the air outlet ends of the converging air flow spaces between thecell covering may be in air flow communication with the diverging airoutlet plenum.

The battery pack apparatus may have a controller operable to adjust aspeed at which the blower operates and at least one temperature sensorlocated on, within, or adjacent at least one of the cell coverings.Thus, the speed of the blower may be adjusted by the controller inresponse to a signal from the at least one temperature sensor. The atleast one temperature sensor may comprise, for example, a firstthermistor located on the cell covering adjacent one end of the batterypack apparatus, a second thermistor located on the cell coveringadjacent an opposite end of the battery pack apparatus, and a thirdthermistor located on the cell covering that is situated about midwaybetween the cell coverings adjacent the ends of the battery packapparatus. In such an arrangement, the speed of the blower may beadjusted based on an average of the signals from the first, second, andthird thermistors.

According to an aspect of this disclosure, a battery pack apparatus maycomprise a plurality of generally flat battery cells and a plurality ofcell coverings with each cell covering being sized to contain twobattery cells. The cell coverings each may have a first planar face anda second planar face. The plurality of cell coverings may be arrangedsuch that the first planar face of each cell covering faces the secondplanar face of an adjacent one of the plurality of cell coverings and isspaced therefrom. In this arrangement of the cell coverings, a pluralityof generally parallel air flow spaces are defined between the pluralityof cell coverings.

According to another aspect of this disclosure, a battery pack apparatusmay comprise a plurality of generally flat battery cells and a pluralityof heat transfer jackets. Each heat transfer jacket may encase at leastone of the plurality of battery cells. The plurality of heat transferjackets may be arranged in spaced apart face-to-face relation and may beconfigured such that a plurality of generally parallel converging airflow spaces are defined between the spaced apart faces of adjacent heattransfer jackets. The battery pack apparatus may also have a blower, anair inlet duct covering a first side of the plurality of heat transferjackets, and an air outlet duct covering a second side of the pluralityof heat transfer jackets. The air inlet duct may be shaped to define aconverging air inlet plenum that becomes narrower in a direction from afirst end of the battery pack apparatus toward a second end of thebattery pack apparatus. In contrast, the air outlet duct may be shapedto define a diverging air outlet plenum that becomes wider in adirection from the first end of the battery pack apparatus toward thesecond end of the battery pack apparatus. Each of the air flow spacesdefined between the heat transfer jackets may be in air flowcommunication with the first and second plenums.

An apparatus according to the present disclosure may include a batterycooling system for a battery pack of an electric vehicle, such as ahybrid electric vehicle, that uses air as the cooling medium but yet isdesigned to maintain the temperature of each battery cell more uniformalong the surface of the battery cell than is believed to have beenachieved in prior art systems. A feedback control system with one ormore temperature sensors that provide signals which are processed by acontrol circuit or controller to determine whether to adjust the speedat which a blower of the system operates may be included in such anapparatus.

Further according to this disclosure, a leading edge of each of the cellcoverings may be covered by a respective insulator, such as foam tapefor example, in the region of the cell coverings near the air inlet endsof the converging air flow spaces. The regions of the first and secondplanar faces near the leading edges of each of the cell coverings may berecessed to accommodate respective portions of the insulator. Thus, eachof the insulators may wrap around the lead edges of the respective cellcoverings. The presence of the insulator may minimize a thermal fineffect at the leading edge of the cell coverings which would otherwisehave a tendency to generate cool spots in the battery cells within thecell coverings near the leading edges of the battery cell units.

Additional features, which alone or in combination with any otherfeature(s), such as those listed above and those listed in the appendedclaims, may comprise patentable subject matter and will become apparentto those skilled in the art upon consideration of the following detaileddescription of illustrative embodiments exemplifying the best mode ofcarrying out the embodiments as presently perceived.

BRIEF DESCRIPTION OF THE DRAWINGS

The detailed description particularly refers to the accompanyingfigures, in which:

FIG. 1 is a perspective view of a portion of a hybrid electric vehicleshowing a lower chassis of the vehicle, an internal combustion enginelocated at a front region of the lower chassis, an electric motorlocated at a rear region of the chassis and coupled to the rear wheels,and a battery pack located at a middle region of the lower chassis;

FIG. 2 is a cross sectional diagrammatic view showing a battery packapparatus having a housing shaped to define a converging air inletplenum and a diverging air outlet plenum, the battery pack apparatushaving a plurality of battery cell units situated between the air inletplenum and the air outlet plenum, each of the battery cell units havingangled planar faces, and the battery cell units being oriented ingenerally parallel spaced apart relation in the housing such that aplurality of converging air flow spaces are defined between the angledplanar faces of adjacent battery cell units;

FIG. 3A is a diagrammatic top view of an alternative embodiment of abattery cell arrangement for a battery pack showing a plurality ofbattery cells of generally rectangular cross section, and a plurality ofvarying thickness walls, each varying thickness wall being situatedadjacent one side of a respective battery cell, a spacer rib extendingbetween each varying thickness wall and the next adjacent battery cell,and the varying thickness walls being oriented such that a plurality ofconverging air flow spaces are defined between the varying thicknesswalls and the next adjacent battery cells;

FIG. 3B is a diagrammatic perspective view of a portion of one of thebattery cells of FIG. 3A, a portion of a first of wall of varyingthickness (in solid) on one side of the battery cell, the portion of thefirst wall of varying thickness having a pair of spacer ribs extendingtherefrom in a cantilevered manner, and a second wall (in phantom) thatmay optionally be included on an opposite side of the battery cell fromthe first wall in some embodiments;

FIG. 4 is a perspective view of a battery pack apparatus showing an airinlet header extending along a side of the battery pack, first andsecond end plates at opposite ends of the battery pack apparatus, and atop plate assembly with a plurality of brackets that provide positiveand negative terminal connection points for battery cells of the batterypack apparatus;

FIG. 5 is a perspective view of the battery pack apparatus, similar toFIG. 4 but with the air inlet header removed, showing the top plateassembly exploded up and away from a plurality of stacked battery celltrays or cassettes that are sandwiched between the end plates of thebattery pack apparatus, each of the battery cell cassettes beingvertically oriented, and positive and negative terminal tabs of thebattery cells that are contained within the cassettes extending upwardlythrough openings provided at the top of each of the battery cellcassettes;

FIG. 6 is a top plan view of the top plate assembly and the first andsecond end plates of the battery pack apparatus;

FIG. 7 is a front elevation view of the first end plate;

FIG. 8 is a side elevation view of the first and second end plates andthe plurality of battery cell cassettes that are sandwiched between thefirst and second end plates;

FIG. 9 is a cross sectional view, taken along line 9-9 of FIG. 7,showing that each of the battery cell cassettes contain two batterycells within an internal space of each cassette and showing a pair ofdummy cassettes or trays that have no battery cells contained thereinand that are situated adjacent respective ones of the end plates;

FIG. 10 is an enlarged cross sectional view, taken along dotted line 10of FIG. 9, showing the terminal tabs of the pair of battery cells withineach of the battery cells cassettes merged together at their upper endsand showing the merged terminal tabs extending upwardly throughrespective openings in the top plate assembly into juxtaposition with arespective terminal connection points of the brackets of the top plateassembly for coupling thereto;

FIG. 11 is an exploded perspective view showing the first and second endplates exploded away from four coupling bars of the battery packapparatus and showing several of the battery cell cassettes alsoexploded away from the coupling bars, the exploded away battery cellcassettes being separated into first and second tray-like shell halveswith the pair of battery cells of each battery cell cassette situatedbetween respective shell halves, and showing several of the batteryshell cassettes remaining mounted on the coupling bars;

FIG. 12 is an exploded perspective view showing further details of thetray-like shell halves of the battery cell cassette and the associatedbattery cells;

FIG. 13 is a front elevation view of one of the tray-like shell halvesshowing a plurality of circular pedestal landings arranged in a gridpattern on a front face of the shell half and showing a recess in eachof the sides of the shell half such that a pair of upper ears areprovided above the recesses and a pair of lower ears are provided belowthe recesses, each upper and lower ear having a rectangular aperturethat is sized to receive a respective one of the four coupling bars;

FIG. 14 is a side elevation view of the tray-like shell half of FIG. 13;

FIG. 15 is a rear elevation view of the tray-like shell half of FIGS. 13and 14;

FIG. 16 is top plan view of the tray-like shell half of FIGS. 13-15;

FIG. 17 is a front elevation view of the other of the tray-like shellhalves showing a plurality of circular pedestals or posts arranged in agrid pattern on a front face of the shell half and showing a recess ineach of the sides of the shell half such that a pair of upper ears areprovided above the recesses and a pair of lowers ears are provided belowthe recesses, each upper and lower ear having a rectangular aperturethat is sized to receive a respective one of the four coupling bars;

FIG. 18 is a side elevation view of the tray-like shell half of FIG. 17;

FIG. 19 is a rear elevation view of the tray-like shell half of FIGS. 17and 18;

FIG. 20 is top plan view of the tray-like shell half of FIGS. 17-19;

FIG. 21 is a diagrammatic view of an air flow control system of thebattery pack apparatus, the air flow control system having a pluralityof temperature sensors that, in use, are mounted to respective batterycell cassettes, a battery management system having circuitry thatreceives signals from each of the temperature sensors, and an adjustablespeed fan which the battery management controls based on the signalsreceived from the temperature sensors;

FIG. 22 is a front elevation view of a portion of an alternativetray-like shell half of an alternative embodiment battery cell cassetteshowing posts or pillars that are in a skewed arrangement on a planarface of the shell half relative to the sides of the shell half to reducethe formation of horizontal hot zones; and

FIG. 23 is a cross-sectional view of a portion of an alternative batterycell unit, taken along a plane that is perpendicular to the planar facesof the heat transfer jacket around the battery cells and that is locatedabout half way between the top and bottom of the battery cell unit,showing recesses in the planar faces near a leading edge of the heattransfer jacket to accommodate foam insulation tape that is providedalong the leading edge.

DETAILED DESCRIPTION

A portion of an automotive vehicle 10 is shown in FIG. 1 and includes alower chassis 12, an internal combustion engine 14 located at a frontregion 16 of the lower chassis 12, and an electric motor 18 located at arear region 20 of the chassis 12. Engine 14 is coupled to front wheels22 of vehicle 10 via a conventional transmission system (not shown)and/or transaxle system (not shown) as is well known in the art topropel the front wheels 22. In the illustrative example, the electricmotor is coupled to the rear wheels 24 via a gear reducer ortransmission assembly 26 and axle arrangement 28. A battery packapparatus 30 (sometimes referred to herein as just a “battery pack”) islocated at a middle region of the lower chassis 12 in the illustrativeembodiment as shown in FIG. 1. In other embodiments contemplated herein,battery pack 30 is mounted elsewhere in the vehicle, such as at thefront region 16 or rear region 20 to chassis 12.

Vehicle 10 has a recharging receptacle 25 which is coupleable to anexternal power source (not shown) to recharge battery pack 30. A batterymanagement system controller 27 is coupled to recharging receptacle 24and contains the circuitry that controls the recharging of battery pack30 as well as controlling the operation of a battery cooling system asdiscussed in further detail below in connection with FIG. 21. Vehicle 10also has a hybrid system controller 29 which contains the electricalcircuitry that controls the operation of engine 14 and electric motor18. A gas tank 31 is provided for storing gasoline used to power theinternal combustion engine 14.

The present disclosure is focused primarily on aspects of battery pack30 and particularly, is focused on aspects of convectively coolingbattery pack 30 with air. Thus, the details of vehicle 10 provided inconnection with FIG. 1 are provided only for general backgroundinformation and to provide a general understanding of the environment inwhich illustrative battery pack 30 may be used. FIGS. 2 and 3 illustratediagrammatically the basic concept of convective air cooling employed incontemplated embodiments and FIGS. 4-20 show the details of anillustrative embodiment and its various components. FIG. 21 is a blockdiagram of an electrical control system associated with the batterypack. Additional details of vehicle 10 can be found in U.S. applicationSer. No. 12/271,194 filed Nov. 14, 2008, U.S. Provisional App. No.61/214,240 filed Apr. 21, 2009, and U.S. Design application No.29/335,696 filed Apr. 20, 2009, each of which is hereby incorporated byreference herein. Vehicle 10 may be, for example, the Bright AutomotiveIDEA vehicle.

In the illustrative example, battery pack 30 is shown being used inconnection with a parallel, road-coupled, plug-in hybrid electricvehicle. However, it should be understood that battery pack 30 accordingto this disclosure can be used with other types of electric vehiclessuch as pure electric vehicles that have no internal combustion engineswhatsoever, as well as serial hybrid electric vehicles in which aninternal combustion engine is used to provide energy for recharging thebattery pack 30 but is not otherwise used to drive the wheels of thevehicle.

Still referring to FIG. 1, battery pack 30 is oriented in a longitudinaldirection with respect to chassis 12 in the illustrative example. Thatis, a long dimension of the overall battery pack is generally parallelwith a long dimension of vehicle 10 and/or chassis 12. In otherembodiments, this need not be the case and battery pack 30 may beoriented in a lateral or side-to-side direction with respect to chassis12 and/or vehicle 10, for example. This is not to exclude thepossibility that an alternative battery pack according to thisdisclosure may be square shaped having length and width dimensions thatare substantially equal. It is also possible that, in some embodiments,battery pack 30 may be oriented vertically such that its long dimensionis oriented vertically, if desired. In other words, it is contemplatedby this disclosure that battery pack 30 and variants thereof may belocated anywhere on vehicle 10 and oriented in any desired manner at thediscretion of the vehicle designer.

Referring now to FIG. 2, battery pack apparatus 30 has a housing 32 witha first side wall 32 configured to define a converging air inlet plenum36 and a second side wall 38 configured to define a diverging air outletplenum 40. Battery pack apparatus 30 also has a plurality of batterycells units 42 situated between air inlet plenum 36 and air outletplenum 40. Each of the battery cell units 42 has first and secondgenerally planar faces 44, 46. Battery cell units 42 are oriented ingenerally parallel spaced apart relation in the housing 32 such that aplurality of converging air flow spaces 48 are defined between thegenerally planar faces 44, 46 of adjacent battery cell units 42.

Each of the battery cell units 42 has a first end 50 adjacent air inletplenum 36 and a second end 52 adjacent air outlet plenum 40. Thus,converging air inlet plenum 36 is considered to exist in the spacebetween wall 34 and a plane defined by first ends 50 of battery cellunits 42. Similarly, the diverging air outlet plenum is considered toexist in the space between wall 38 and a plane defined by the secondends 52 of battery cell units 42. Converging air flow spaces 48 betweenbattery cell units 42 are in air flow communication with the inlet andoutlet plenums 36, 40 and extend laterally with respect to battery pack30 in substantially perpendicular relation with the planes defined bythe ends 50, 52 of the battery cell units. Additional converging airflow spaces 48′ are defined in the spaces between a first end wall 54 ofhousing 32 and planar face 44 of the next adjacent battery cell unit 42and between a second end wall 56 of housing 32 and planar face 46 of thenext adjacent battery cell unit 42. In the illustrative example, wall 54is parallel with wall 56 such that the geometry of air flow spaces 48′are slightly different than the geometry of air flow spaces 48, but thisneed not be the case in other embodiments. For example, walls 54, 56 maybe configured such that air flow spaces 48′ have the same geometry asair flow spaces 48, if desired.

The terms “converging” and “diverging” as used herein, including in theclaims, are intended to be with respect to the general direction of airflow through the associated space. Thus, for example, if an air passageor air space is said to be “converging” it means that the passage orspace is generally narrowing in the direction of air flow. In contrast,if an air passage or air space is said to be “diverging” it means thatthe passage or space is generally widening in the direction of air flow.Thus, in general, from any particular location within an air space, a“converging” air space will be wider at upstream locations of the spaceand narrower at downstream locations of the space, whereas a “diverging”air space will be wider at downstream locations of the space andnarrower at upstream locations of the space. Furthermore, it is withinthe scope of this disclosure for the battery cell units 42 to haveregions near the inlets and outlets of the air flow spaces that arerounded or chamfered such that a relatively small portion of the airflow space widens in the direction of air flow at the outlet, but yet,in such examples, the overall air flow spaces are still considered to bediverging between the inlet and outlet ends of the air flow spacesaccording to this disclosure.

In the illustrative example shown in FIG. 2, inlet air moves through amain inlet opening 58 of housing 32 in a direction indicated by arrow 60and advances through converging air inlet plenum 36 with portions of theinlet air being forced into the various air flow spaces 48 for movementthrough the spaces 48 in the directions indicated by the series ofgenerally parallel arrows 62. As the inlet air moves through inletplenum 36 from inlet opening 58 toward end wall 56 of housing 32, heatis convectively transferred from ends 50 of battery cell units 42 to thestream of air moving through air inlet plenum 36. Furthermore, as theair moves through air flow spaces 48 in the directions of arrows 62,heat is convectively transferred from planar faces 44, 46 of batterycell units 42 to the moving air. The heated air exits air flow spaces 48between battery cell units 42, enters air outlet plenum 40, and advancesthrough outlet plenum to an air outlet 64 of housing 32 where the heatedair exits housing 32 as indicated by arrow 66 in FIG. 2.

The further that the inlet air moves through the converging air inletplenum 36 and the further that the air moves through converging airspaces 48 between battery cell units 42, the more that the air has atendency to be heated due to the increasing exposure of the air streamto the heated surfaces of battery cell units 42. However, because plenum36 and air spaces 48 are converging spaces, the velocity of the air nearthe respective downstream ends of these spaces 36, 48 is faster than thevelocity at the respective upstream ends of these spaces. However, thecombination of the increasing air velocity and the converging air flowspaces 36, 48 results in the general overall effect of having asubstantially constant flow rate (liter per minute) of air throughoutthe length of the converging passage. This compensates for theconvective heating of the air as it moves through spaces 36, 48. The airoutlet plenum 40 diverges so that an inappropriate amount of backpressure within housing 32 is avoided.

Based on the foregoing, it will be appreciated that the convection ishigher or stronger near the exit end of air spaces 48 with the warmed-upair because the heat transfer boundary layer is getting thinner alongthe length of the air spaces 48 in the direction of air flow. Theconvection is lower or weaker near the inlet end of air spaces 48. Withweak convection, the temperature difference between surfaces 44, 46associated with a particular air space 48 and the local or adjacent airmight be around 8° C. in some embodiments, such that if air entered theparticular air flow space 48 at 20° C., for example, then surfaces 44,46 would be about 28° C. near the inlet. Then, near the outlet of theparticular air flow space 48, the thinner boundary layer due to the“squeezing” of the moving air may result in a temperature differencebetween surfaces 44, 46 and the local or adjacent air being around 2°C., for example. However, because the moving air has traveled past amajority of cells 42 at the outlet end of the particular air space 48,the air has heated to about 26° C., for example. Thus, 26° C. for theair plus 2° C. for convection delta T results in surfaces 44, 46 beingabout 28° C. which is the same as near the inlet of the particular airspace 48.

In connection with FIG. 2, it should be appreciated that this is adiagrammatic cross sectional view and that the cross sectional shape ofhousing 32 and battery cell units 42 is contemplated as being maintainedinto and out of the page for a substantial portion of the depth ofbattery pack apparatus 30. Depending upon the amount of heat generatedby battery cell units 42, it is contemplated by this disclosure that itis possible to fashion the convergence geometry of plenum 36 and theconvergence geometry of air flow spaces 48 between walls 44, 46 ofbattery cell units 42, as well as the divergence geometry of outletplenum 40, and to control the flow rate of air into air plenum 36 in amanner that results in the temperature across the faces 44, 46 ofbattery cell units 42 remaining substantially uniform between theleading edges and trailing edges of the battery cell units. In thisregard, for some embodiments, the temperature is considered to besubstantially uniform if the temperature gradient along the faces 44, 47of battery cell units 42 from their leading edges to their trailingedges is no more than 3° Celsius. The leading edges of battery cells 42are those regions or areas where faces 44, 46 meet respective first ends50 and the trailing edges of battery cells 42 are those regions or areaswhere faces 44, 46 meet second ends 52. In some embodiments, theseleading and trailing edges may be rounded or chamfered as alluded topreviously in this disclosure.

Many battery cells for use in automotive vehicles have generallyrectangular cross sections when the cells are sectioned in a directionperpendicular to their large parallel main planar faces and their sides,as is the case with battery cells 68 shown in FIGS. 3A and 3B. Batterycells 68 like those shown in FIGS. 3A and 3B are sometimes referred toas prismatic battery cells and may be of the lithium ion variety. Oneexample of such battery cells 68 are Model No. F014 battery cellsavailable from EIG Ltd. of South Korea but similar types of batterycells are available from other manufacturers. These types of batterycells are sometimes referred to as “pop tarts” by those in the art sincethey are packaged in metal foil and have a tendency to resemble thebreakfast food known by the same name.

According to this disclosure, however, battery cells for use in batterypack 30 may be constructed having generally elongated, trapezoidal crosssections like battery cell units 42 of FIG. 2. In such embodiments, noadditional external coverings or jackets are needed to create theangled, non-parallel planar faces 44, 46 because the battery cellsthemselves are constructed with the appropriate cross sectional shapeduring manufacture to form converging air spaces 28 therebetween whenplaced in spaced apart, face-to-face relation. According to thisdisclosure, however, when battery cells 68 of rectangular cross sectionare used in battery pack 30, then appropriately shaped cell coveringsmay be situated adjacent the battery cells to create the desiredconverging air flow spaces. Such an example is shown in FIGS. 3A and 3Bin which battery cells 68 have cell coverings 70.

Referring still to FIGS. 3A and 3B, each of the cell coverings 70 has avarying thickness wall 72 which increases in thickness from an air inletend 74 of the associated battery cell 68 to an air outlet end 76 of theassociated battery cell 68. Illustrative cell coverings 70 also have aset of spacers or ribs 78, two of which are shown in FIG. 3B, thatextend outwardly in a cantilevered manner from a planar face 80 of cellcovering 70. Ribs 78 each have an outer edge 82 that engages a planarface 84 of the next adjacent battery cell 68. Suitable fasteners, suchas layers of adhesive, are used to couple cell coverings 70 to batterycells 68 in some embodiments. Other types of fasteners, such as clips,caps, straps, bands, etc., may be used alone or in combination with anyother types of fasteners, to couple battery cells 68 and cell coverings70 together in other embodiments, if desired.

Cell coverings 70 are sized and configured so that converging air flowspaces 86 are defined between planar faces 80 of cell coverings 70 andplanar faces 84 of the next adjacent battery cells 68. According to thisdisclosure, housing 32 of battery pack 30 shown in FIG. 2 may contain astacked arrangement of battery cells 68 with cell coverings 70therebetween in lieu of battery cell units 42. In such an arrangement,inlet air enters converging air flow spaces 86 adjacent first ends 74 ofbattery cells 68 as indicated by arrows 88 shown in FIG. 3A and outletair exits from converging air flow spaces 86 adjacent second ends 76 ofbattery cells 68 as indicated by arrows 90. According to thisdisclosure, cell coverings 70 may be made from a plastics material orfrom a metal material, such as aluminum.

In the illustrative example of FIGS. 3A and 3B, one planar face 84 isleft exposed to the associated air flow space 86 whereas the oppositeplanar face of battery cell 68 is covered by a respective cell covering70. In an alternative embodiment, planar faces 84 of battery cells 68may also be covered by a cell covering 70′ as shown in FIG. 3B (inphantom). In such an alternative embodiment, planar faces 72, 72′ ofrespective cell coverings 70, 70′ are oriented substantially similar toplanar faces 44, 46 of battery cell units 42 of FIG. 2. Also, in somesuch alternative embodiment, the geometry of spacers 78 are adjustedaccordingly so that edges 82 are oriented properly to engage faces 72′of the next adjacent cell covering. Other spacer geometries arepossible, such as for example, having spacers 78 configured so thatedges 82 of adjacent ribs 78 contact each other or having the spacers 78that extend from face 72 of cell covering 70 being staggered in heightas compared to the spacers (not shown, but similar to ribs 78) extendingfrom face 72′ of cell covering 70′. As was the case with the embodimentof FIG. 2, in the embodiment of FIGS. 3A and 3B (as well as the variantsthereof), the increasing rate of air flow through air flow spaces 86 dueto the converging shape of these spaces 86 helps to maintain a fairlyuniform temperature across battery cells 68 from the first ends 74 tothe second ends 76 thereof.

Referring now to FIGS. 4-20, additional details of one embodiment ofbattery pack apparatus 30 are shown. Battery pack 30 has a top plateassembly 92 situated atop a stacked row or array of battery cell units42 as shown, for example, in FIGS. 4 and 5. The battery cell units 42shown in FIGS. 5 and 8-12 are sometimes referred to herein as batterycell trays 42 or battery cell cassettes 42. Top plate assembly 92 has agenerally flat and rectangular top wall 94 that supports a row of wideU-shaped brackets 96, a row of narrow U-shaped brackets 98, a positiveterminal bracket 100 and a negative terminal bracket 102 as shown, forexample, in FIGS. 4-6.

Battery pack 30 has a first and second end plates 110 located at theopposite ends of the battery pack 30 as shown, for example, in FIGS. 4and 5. Battery pack 30 also has an air inlet header 112, shown in FIG.6, adjacent one side of battery pack 30 and an air outlet header 114,shown in FIGS. 4 and 6, adjacent an opposite side of battery pack 30.Air inlet header 112 includes sidewall 34 and air outlet header includesside wall 38. Thus, air inlet header 112 is shaped to provide batterypack 30 with its converging air inlet plenum 36 and air outlet header 38is shaped to provide battery pack 30 with its diverging air outletplenum 40. In the illustrative embodiment, end plates 110 are made ofsteel and headers 112, 114 are made from a plastics material such asNoryl GTX 810. However, it is within the scope of this disclosure forend plates 110 and headers 112, 114 to be made from any material havingsuitable strength, such as aluminum, for example. Composite materialscan be used to make end plates 110 and headers 112, 114, if desired.

Battery pack has a pair of end trays 116 each of which is situatedadjacent a respective end plate 110 as shown in FIGS. 5, 8 and 9. Endtrays 116 are sometimes referred to herein as dummy trays 116. Each endtray 116 has a pair of threaded bores 118, one of which can be seen inFIG. 5, formed at its upper end. Top plate 114 has four apertures 120,each of which is aligned with a respective bore 118. Bolts 122 extendthrough apertures 120 and are threaded into bores 118 of end trays 116to fasten top plate assembly 92 in place on battery pack 30. Washers 124are interposed between the heads of bolts 120 and plate 94 in theillustrative example.

In some embodiments, a generally flat rectangular bottom plate (notshown) is provided and fastens to the bottom of end trays 116 in asimilar manner. Plate 94 has a series of apertures 126, shown best inFIG. 6, along each of the opposite side edges thereof that receivesuitable fasteners, such as bolts similar to bolts 122, to fastenheaders 112, 114 in place on battery pack 30. In those embodimentshaving a bottom plate, apertures similar to apertures 126 of plate 94are provided for receipt of additional fasteners to further fastenheaders 112, 114 in place.

As mentioned above, battery pack 30 has a stacked array of battery celltrays 42. As shown best in FIG. 12, each battery cell tray 42 has afirst tray half 130 and a second tray half 132. Each tray half 130, 132has a generally rectangular recess 134 such that, when the tray halves130, 132 are mated together, an internal space is provided by therecesses 134 for receiving first and second battery cells 68. Trayhalves 130, 132 are generally rectangular and each have a top wall 136,a bottom wall 138, and a pair of side walls 140 interconnecting the topand bottom walls 136, 138. The walls 136, 138, 140 of tray halves 130,132 from a rim that surrounds recess 134. However, top wall 136 of eachtray half is formed to include two notches 142. When tray halves 130,132 are joined together, the notches 142 cooperate with each other toprovide a pair of openings (referred to herein as “openings 142”)through which positive terminal tabs 144 and negative terminal tabs 146of battery cells 68 extend.

Side walls 140 are each formed to include a cutout or recess 144 asshown in FIG. 12. Recesses 144 are configured such that tray halves 130,132 have a pair of upper ears 146, each of which is situated above arespective recess 144, and a pair of lower ears 148, each of which issituated below a respective recess 144. Each ear 146, 148 has agenerally rectangular aperture 150 extending therethrough. The ears 146,148 of first tray half 130 each have a depression or recess 152 as shownfor example in FIG. 17, and the ears 146, 148 of second tray half 132each have a protrusion 154 as shown in FIGS. 12-14 and 16. When thebattery cell units 42 are stacked together, the protrusions 154 of eachtray half 132 are received in the depressions 152 of the next adjacenttray half 130 except for the battery cell units 42 at the extreme endsof battery pack 30, in which case the depressions 152 of the batterycell unit 42 at one end of battery pack 30 receive appropriatelyconfigured protrusions that extend from one of dummy trays 116 and theprotrusions 154 of the battery cell unit 42 at the opposite end ofbattery pack 30 are received in appropriately configured depressions ofthe other of the dummy trays 116.

In the illustrative example, three out of four of the depressions 152 ofeach tray half 130 are circular in shape and the fourth depression 152is oval in shape. Similarly, three out of four of the protrusions 154are circular in shape and the fourth protrusion is oval in shape. Thenon-round depressions 152 and protrusions 154 of the battery cell units42 assure that the battery cell units 42 are stacked together in theproper orientation.

Each of the ears 146, 148 of each tray half 130 has an L-shaped groove158, as shown in FIGS. 12 and 19, and each of the ears 146, 148 of eachtray half 132 has an L-shaped rib 160, as shown in FIGS. 14-16. When thetray halves 130, 132 are mated together, each rib 160 is received in arespective groove 158 to help maintain tray halves 130, 132 in properalignment with one another. When the tray halves 130, 132 are matedtogether, a cell covering or heat transfer jacket 131 is formed and hasa peripheral seam 156 that extends around the top, bottom and sides ofthe cell covering 131.

Each tray half 130 includes first planar face 44 and each tray half 132includes second planar face 46. The front walls of tray halves 130, 132which provide planar faces 44, 46, respectively, have varying thicknessso that when battery cell units 42 are stacked a plurality of generallyparallel converging air flow spaces 48, a portion of which are shown inFIG. 10, are formed. In some embodiments, tray halves 130, 132 are madefrom a plastics material such as Noryl GTX 810 material. However, trayhalves 130, 132 may be made from other materials, such as aluminum whichhave suitable strength and heat transfer characteristics.

In one embodiment, the spacing or gap between the confronting planarfaces 44, 46 that define air flow spaces 48 is about 2.5 millimeters(mm) at the inlet end and is about 0.5 mm at the outlet end. However,other embodiments in which the spacing between battery cell units 42 islarger or smaller than the given example are within the scope of thisdisclosure. It has been found that suitable battery cooling can beachieved with a ratio of inlet gap size to outlet gap size of about 4 to5. Of course, other factors such as fan or blower capacity and ambientair temperature play a role, and so other ratios of inlet to outlet gapsize may be suitable in other embodiments. Air flow spaces 48′, one ofwhich is shown in FIG. 10, are located between battery cell units 42 anddummy trays 116 at the opposite ends of battery pack 30 and haveslightly different geometries than air flow spaces 48. The front andrear faces of dummy trays 116 are parallel and so, in the illustrativeexample, air flow spaces 48′ are roughly half the size of air flowspaces 48.

Each first tray half 130 has a plurality of standoffs 162 extending awayfrom planar face 44 and each second tray half 132 has a plurality ofstandoffs 164 extending away from planar face 46. In the illustrativeembodiment, standoffs 162 are posts or pedestals (sometimes referred toherein as posts 162 or pedestals 162) and standoffs 164 are postreceivers or pedestal receivers (sometimes referred to herein as postreceivers 164 or pedestal receivers 164). Posts 162 are frustum conicalshaped protrusions in the illustrative example, but may have othershapes, such as cylindrical, in other embodiments. Post receivers 164are generally cylindrical ring shaped protrusions in the illustrativeexample. Pedestals 162 and pedestal receivers 164 are arranged in a gridpattern on the respective planar faces 44, 46 as shown in FIGS. 13 and17, for example. When the battery cell cassettes 42 are stackedtogether, each pedestal 164 is received in a companion pedestal receiver164 except for the battery cell cassettes 42 at the extreme ends ofbattery pack 30 in which case the pedestals 162 and pedestal receivers164 are received in depressions 166 formed in the dummy trays 116 asshown in FIG. 9.

When the battery cell units 42 are stacked together, the rectangularapertures 150 in the upper and lower ears 146, 148 are aligned andbattery pack 30 has four coupling rods or bars 168, each of whichextends through a respective set of the aligned apertures 150 as shownbest in FIG. 11. Dummy trays 116 also have ears with apertures that aresimilar to ears 146, 148 and apertures 150 of battery trays 42 and thatreceive rods 168. The end regions of coupling rods 168, which extendbeyond dummy trays 116, are necked down and have threaded apertures thatare aligned with respective holes 170 provided in side walls 172 of endplates 110. Bolts 174 extend through holes 170 into threaded engagementwith the apertures provided at the ends of coupling bars 168. Thus,coupling bars 168 hold the stacked array of battery trays 42, as well asdummy trays 116, in place between end plates 110.

As previously mentioned, the internal space formed by recesses 134 oftray halves 130, 132 of each battery cell unit 42 receives two batterycells 68 therein. Each battery cell 68 has a positive terminal tab 176and a negative terminal tab 178 as shown, for example, in FIG. 12. Topplate assembly 92 has a plurality of slots or openings 180 as shown inFIGS. 4-6. Tabs 176, 178 extend upwardly from the main body of batterycells 68 through respective holes defined by notches 142 provided in topwalls 136 of tray halves 130, 132 and through slots 180 of top plateassembly 92 into juxtaposition with respective upstanding portions ofU-shaped brackets 96, 98, with the exception of the tabs 176 associatedwith positive terminal bracket 100 and tabs 178 associated with negativeterminal bracket 102. Tabs 176, 178 are attached, such as by ultrasonicwelding, to respective brackets 96, 98, 100, 102.

The orientation of battery cells 68 within cell coverings 131 alternatesfrom battery cell unit 42 to battery cell unit 42. Thus, each bracket96, 98 electrically couples the positive terminal tabs 176 of thebattery cells 68 of one battery cell unit 42 to the negative terminaltabs 178 of the battery cells 68 of the next adjacent battery cell unit42 as shown in FIG. 10 with regard to one of brackets 98. In theillustrative embodiment, battery pack 30 has forty eight battery cells68 contained in pairs within twenty four cell coverings 131. However, itis within the scope of this disclosure for more or less battery cells68, as well as more or less cell coverings 131, to be included in abattery pack.

With the inlet and outlet headers removed, battery pack 30 of FIGS. 4-20has an overall length of about 555.5 mm, a height of about 284.2 mm, anda width of about 220 mm. Tray halves 130, 132 are about 236.5 mm inheight, 203 mm in width, and 9.35 mm in depth (not including the standoffs 162, 164). Thus, the depth of a cell covering is about 18.7 mm. Thedummy trays are made of an insulator material such as aluminum or aplastics material. The end plates 110 and coupling rods 168 are made ofsteel. The sizes and materials described above with regard to the FIG.4-20 embodiment of battery pack 30 are not intended to be limiting.Thus, battery packs 30 of any suitable size and shape made from anysuitable materials are intended to be within the scope of thisdisclosure.

As mentioned previously, vehicle 10 has a battery management systemcontroller 27. As shown diagrammatically in FIG. 21, a plurality oftemperature sensors 182 are coupled to battery management system 27 toprovide input signals thereto. The temperature sensors 182 are mountedto various ones of the cell coverings 131 of battery cell units 42 ofbattery pack 30. In one embodiment, temperature sensors 182 are mountedto the cell coverings 131 of the battery cell units 42 at the extremeends of battery pack and at least one additional temperature sensor ismounted to one of the battery cell units 42 in the middle region ofbattery pack 30. Temperature sensors 182 are thermistors in someembodiments.

Based on the input signals from the temperature sensors 182, controller27 adjusts the speed of an adjustable speed blower or fan 184. Forexample, in some embodiments, controller 27 adjusts the duty cycle of apulse width modulated (PWM) output signal that is used to control thespeed of fan 184. Controller 27 is programmed so that, if thetemperature sensed by any single sensor 182 exceeds a threshold value,the speed of the fan 184 is increased. In addition, controller 27 isprogrammed to calculate difference values between the temperaturesindicated by the various temperature sensors 182 and if any of thecalculated difference values exceed a difference threshold, the speed ofthe fan 184 is increased. This facilitates keeping the temperatures ofall of the battery cells 68 relatively uniform. Thus, controller 27,temperature sensors 182 and fan 184 serve as an air flow control systemfor the battery pack 30. If the temperatures sensed by sensors 182 andthe calculated temperature differences are all below the respectivethresholds, then controller 27 incrementally decreases the speed of fan184 at predetermined time intervals so as to reduce the amount of powerexpended on operating the fan 184.

Referring now to FIG. 22, a portion of an alternative tray half 230 ofan alternative embodiment battery cell cassette is shown. Tray half 230is similar to the tray half 130 described above and so like referencenumerals are used to denote portions of tray 230 that are substantiallysimilar to tray half 130. The main difference between tray half 130 andtray half 230 is that the grid pattern of posts or pillars 262 of trayhalf 230 are skewed at an angle 250 on planar face 44 of tray half 230relative to top edge 136 and bottom edge (not shown of tray half 230. Inthe illustrative example, the angle 250 at which the rows of pedestalsare skewed relative to the top and bottom edges is about 15° as shown inFIG. 22. However, it is within the scope of this disclosure for posts262 to be skewed at other angles, such as angles that are greater thanor less than 15°. In contrast, the rows of posts 162 of tray half 130,shown in FIG. 17, are parallel with the top wall 136 and bottom wall 138and are perpendicular to the side walls 140 of tray half 130.

Skewing the rows of posts 262 of tray half 230 by angle 250 relative tothe top wall 136 and bottom wall (not shown) also skews the rows ofposts 262 relative to the direction of air flow which air flow isgenerally parallel with the top and bottom walls of tray half 130 asindicated by the series of arrows 260 in FIG. 22. The skew pattern ofposts 262 enhances scattering of the air flow through the associated airflow space thereby enhancing the convective cooling by reducing thetendency that hot spaces can form in horizontal zones between the posts262. Thus, in the illustrative example, the post pattern is anequilateral triangle matrix skewed to the direction of air flow. Also,in the illustrative example, the posts 262 at the outer boundary of thepost grid pattern are located on the planar face 44 at least onediameter inwardly away from the battery cell envelope 264.

It will be appreciated that the tray half (not shown) adjacent to trayhalf 230 has post receivers, sometimes referred to as craters, skewed ina complementary pattern to receive the posts 262 of tray half 230. Insome embodiments, the top region of planar face 44 above battery cellenvelope 264 and the bottom region of planar face 44 below battery cellenvelope 243 is shaped as a raised ramp that forms a 0.7 mm gap with anadjacent cell face. That is the top and bottom regions of tray half 230in the areas above and below the portion of planar face 44 that has theposts 262 serve as seal foundations with raised ramps.

Referring now to FIG. 23, a portion of an alternative battery cell unit342 is shown in cross section. Battery cell unit 342 has alternativetray halves 330, 332 which each have a recess 350 formed in therespective planar faces 44, 46 near the leading edge of unit 342. Aninsulator 360 is provided along the leading edge of battery cell unit342 and has portions that are received in the recesses 350 of trayhalves 330, 332. In the some embodiments, insulator 360 comprises foamtape. The insulator 360 extends along the leading edge of unit 342 tocover side walls 140 and recesses 350 of tray halves 330, 332 in theregion of the leading edge between the upper and lower ears (not shown,but similar to ears 146, 148 of unit 42). Thus, a battery cell apparatushaving a plurality of stacked battery cell units 342 with insulators 360wrapped around the lead edges of the respective cell units 342 iscontemplated by this disclosure. By providing insulators 360 at the airinlet end of battery cell units 342, a thermal fin effect at the leadingedge of the cell units 342 is minimized to inhibit generation of coolspots in the battery cells 68 near the leading edges of the battery cellunits. This, in turn, promotes a more uniform temperature in batterycells 68 between the leading and trailing edges of battery cell units342. In one embodiment, the foam tape used has a width of about 8 mm anda thickness of about 1 mm.

It is contemplated by this disclosure that, in some embodiments,pedestal receivers are omitted such that pedestals or posts 162, 262simply abut a flat planar face of the next adjacent battery cell unit.In other embodiments, each planar face of the battery cell unitsincludes posts or pedestals like posts 162, 262. In such embodiments,the posts are arranged to somewhat interlace with one another. That is,each post extending from one planar face of adjacent pairs ofconfronting planar faces contacts the planar face of the other planarface in a space between the posts of that other planar face.

Although certain illustrative embodiments have been described in detailabove, many embodiments, variations and modifications are possible thatare still within the scope and spirit of this disclosure as describedherein and as defined in the following claims.

1. A battery pack apparatus comprising a plurality of generally flatbattery cells, and a plurality of cell coverings, each cell coveringhaving an internal space that receives at least one battery cell, eachof the cell coverings having external first and second planar faces thatface away from the at least one battery cell which is received in therespective internal space, the plurality of cell coverings beingarranged such that the first planar face of each cell covering faces thesecond planar face of an adjacent one of the plurality of cell coveringsand is spaced therefrom, each of the cell coverings being constructedsuch that the first and second planar faces of adjacent cell coveringsdefine a converging air flow space between each adjacent pair of theplurality of cell coverings such that a plurality of generally parallelconverging air flow spaces are defined between the cell coverings, eachof the converging air flow spaces being wider at an air inlet end of theair flow space and narrower at an air outlet end of the air flow space.2. The battery pack apparatus of claim 1, wherein each of the cellcoverings has a plurality of standoffs extending from the first andsecond planar faces to maintain proper spacing between adjacent pairs ofcell coverings.
 3. The battery pack apparatus of claim 2, wherein thestandoffs extending from the first planar face of each cell coveringcomprise a plurality of pedestals and the standoffs extending from thesecond planar face of each cell covering comprises a plurality ofpedestal receivers.
 4. The battery pack apparatus of claim 3, whereinthe pedestals comprise cylindrical portions and the pedestal receiverscomprise annular rings that receive the pedestals.
 5. The battery packapparatus of claim 3, wherein the pedestals and pedestal receivers arearranged to form a grid pattern on the respective first and secondplanar faces.
 6. The battery pack apparatus of claim 2, wherein each ofthe cell coverings including a tray-like first shell half and atray-like second shell half, the first and second shell halves definingthe internal space therebetween and mating together along a peripheralseam.
 7. The battery pack apparatus of claim 1, wherein each of the cellcoverings have first and second sidewalls interconnecting the first andsecond planar faces, the first and second sidewalls having recessesformed therein to define a pair of upper ears situated above therecesses in the first and second sidewalls and a pair of lower earssituated below the recesses in the first and second sidewalls.
 8. Thebattery pack apparatus of claim 7, wherein each of the upper ears andlower ears have an aperture therethrough and further comprising a set ofcoupling bars that extend through the apertures.
 9. The battery packapparatus of claim 8, wherein the apertures are rectangular in shape andeach coupling rod has a rectangular cross section.
 10. The battery packapparatus of claim 8, further comprising a first end plate and a secondend plate, each of the coupling bars having a first end fastened to thefirst end plate and a second end fastened to the second end plate, andwherein the plurality of cell coverings and the plurality of batterycells are sandwiched between the first and second end plates.
 11. Thebattery pack apparatus of claim 7, wherein each of the upper and lowerears have a protrusion on one side thereof and a depression on anopposite side thereof and wherein the protrusions of the upper and lowerears of each cell covering nest within the depressions of the upper andlower ears of a next adjacent cell covering.
 12. The battery packapparatus of claim 11, wherein at least one of the depressions and atleast one of the protrusions are round in cross section and wherein atleast one of the depressions and a least one of the protrusions arenon-round in cross section.
 13. The battery pack of claims 1, whereinthe internal space of each cell covering receives two battery cells. 14.The battery pack apparatus of claim 13, wherein a top of each cellcovering has a first opening and a second opening, each of the pair ofbattery cells received in the internal space of each cell covering havea positive terminal tab that extends through the first opening of therespective cell covering, and each of the pair of battery cells receivedin the internal space of each cell covering have a negative terminal tabthat extends through the second opening of the respective cell covering.15. The battery pack apparatus of claim 14, further comprising a topplate assembly situated atop all of the cell coverings, the top plateassembly having a first row of openings through which respective pairsof the positive terminal tabs extend, the top plate having a second rowof openings through which respective pairs of the negative terminal tabsextend, and the top plate being configured to electrically connect allof the positive terminal tabs with a main positive stud and toelectrically connect all of the negative terminal tabs with a mainnegative stud.
 16. The battery pack apparatus of claim 1, furthercomprising a blower, an air inlet header situated adjacent a first sideof the cell coverings, and an air outlet header situated adjacent asecond side of the cell coverings, wherein the air inlet header isshaped to define a converging air inlet plenum that narrows in thedirection of air flow produced by the blower, and wherein the air outletheader is shaped to define a diverging air outlet plenum that widens inthe direction of air flow out of the air outlet header.
 17. The batterypack apparatus of claim 16, wherein the air inlet ends of the convergingair flow spaces between the cell coverings are in air flow communicationwith the converging air inlet plenum and the air outlet ends of theconverging air flow spaces between the cell coverings are in air flowcommunication with the diverging air outlet plenum.
 18. The battery packapparatus of claim 17, further comprising a controller operable toadjust a speed at which the blower operates and at least one temperaturesensor located on at least one of the cell coverings, wherein the speedof the blower is adjusted by the controller in response to a signal fromthe at least one temperature sensor.
 19. The battery pack apparatus ofclaim 18, wherein the at least one temperature sensor comprises a firstthermistor located on the cell covering adjacent one end of the batterypack apparatus, a second thermistor located on the cell coveringadjacent an opposite end of the battery pack apparatus, and a thirdthermistor located on the cell covering that is situated about midwaybetween the cell coverings adjacent the ends of the battery packapparatus.
 20. The battery pack apparatus of claim 19, wherein the speedof the blower is adjusted based on an average of the signals from thefirst, second, and third thermistors.
 21. The battery pack apparatus ofclaim 1, wherein a leading edge of each of the cell coverings is coveredby a respective insulator in the region of the cell coverings near theair inlet ends of the converging air flow spaces.
 22. The battery packapparatus of claim 21, wherein the insulator comprises foam tape. 23.The battery pack apparatus of claim 21, wherein regions of the first andsecond planar faces near the leading edges of each of the cell coveringsis recessed to accommodate respective portions of the insulator.
 24. Abattery pack apparatus comprising a plurality of generally flat batterycells, a plurality of cell coverings, each cell covering being sized tocontain two battery cells, the cell coverings each having a first planarface and a second planar face, the plurality of cell coverings beingarranged such that the first planar face of each cell covering faces thesecond planar face of an adjacent one of the plurality of cell coveringsand is spaced therefrom such that a plurality of generally parallel airflow spaces are defined between the plurality of cell coverings.
 25. Abattery pack apparatus comprising a plurality of generally flat batterycells, a plurality of heat transfer jackets, each heat transfer jacketencasing at least one of the plurality of battery cells, the pluralityof heat transfer jackets being arranged in spaced apart face-to-facerelation and being configured such that a plurality of generallyparallel converging air flow spaces are defined between the spaced apartfaces of adjacent heat transfer jackets, a blower, an air inlet ductcovering a first side of the plurality of heat transfer jackets, the airinlet duct being shaped to define a converging air inlet plenum thatbecomes narrower in a direction from a first end of the battery packapparatus toward a second end of the battery pack apparatus, and an airoutlet duct covering a second side of the plurality of heat transferjackets, the air outlet duct being shaped to define a diverging airoutlet plenum that becomes wider in a direction from the first end ofthe battery pack apparatus toward the second end of the battery packapparatus, wherein each of the air flow spaces is in air flowcommunication with the first and second plenums.